Coded track circuit apparatus with insulation breakdown protection



Feb. 26, 1957 c. E. STAPLES CODED TRACK CIRCUIT APPARATUS WITH INSULATION BREAKDOWN PROTECTION Filed Nov. 10-. 1953 A W A l f WT. W Y 4L A Q mu m 4 A. k 5w m M U Q wk mY w 0 B k A L m m w v 1 SF AIQ 5 1 Q EMA w Q h -mm A m HTQ Ea wi & 5e

CODED TRACK CIRCUIT APPARATUS WITH INSULATION BREAKDOWN PROTECTION Crawford E. Staples, Homewood, Pa., assignor to Westinghouse Air Brake Company, Wilmerding, Pa., a corporation of Pennsylvania Application November 10, 1953, Serial No. 391,187

5 Claims. (Cl. 246-34) My invention relates to coded track circuit apparatus for use in railway signaling systems, and particularly to an improved arrangement for coded track circuit app-ara-- tus for repeating energy received from a first track section to a second track section, commonly known in the art as a cut section.

Because of limitations on the length of railway track circuits, due primarily to the effect of the ballast resistance on the energy transmitted through the track circuit, it is at times necessary to provide repeating or cut sections, in which the energy from one track circuit is repeated by suitable apparatus to cause energy to be reapplied at the adjacent end of the adjacent section, so that several track sections may be incorporated in one block section. Moreover, in coded track circuit railway signaling systems, it is often necessary to provide cut sections of the type in which an impulse of energy is supplied to one track circuit at a cut section during the interval between the impulses of energy received from the other track section. Such an arrangement is commonly known in the art as a back contact coding cut section, because-in efiect, the supply of energy to one track section is governed by circuits which in part include the back contacts of the track track circuits become broken down so that energy can flowthrough the insulated joints from one track section to the other. Under such conditions, it will be apparent thatthe supplyof energy to the one track section may cause the track relay which normally controls the supply of this energy to become falsely energized, and since the supply of energy to the one track section is governed over the back contact of the track relay for the other section, a socalled door-bell action may arise, wherein the track relay is energized by a circuit which is governed by its own back contact, so that the contacts of the relay are recurrently operated at some rate depending upon the circuit parameters, the inertia of the moving parts of the relay, etc. Such operation is undesirable in that it falsely creates a code in the repeated track section, which may not be in accordance with the code received from the other section and accordingly, it will be seen that this could create a non-safe condition in that it might cause the clearing of a signal for a trafiic movement into an occupied track section.

It is accordingly an object of my invention to provide improved coded track circuit apparatus for use at back contact coding cut sections, which is constructed and arranged in such manner that the breakdown of insulated joints will not cause operation of the apparatus in an un- Another object of my invention is to provide anim- United tews Patefi ii,;0.. f

2,783,370 Patented r s. as, 1957 proved back contact coded cut section apparatus for railway signaling systems in which the track circuits for one direction are of the polarized type, with the apparatus arranged so that the polarity will be properly maintained on the retransmission of the code through the cut section, and improper operation of the apparatus in the event of breakdown of the insulated joints of the cut section will be avoided.

A further object of my invention is to provide an improved arrangement of apparatus for back contact coding cut sections in a railway signaling system in whichsteady energy must be transmitted through the track sections in either direction at times, and at other times coded energy is supplied through the cut section which is of the polarized type in onedirection and a neutral type in the other direction.

Other objects of my invention and features of novelty thereof will be apparent from the following description taken in connection with the accompanying drawing.

I shall describe one form of coded track circuit apparatus embodying my invention and shall then point out the novel features thereof in claims.

In practicing my invention I provide, at a cut section 'location, code receiving and transmitting means for each adjacent end of the two track sections including track relay means responsive to the energy supplied thereto from the associated track section, and transmitting means including transmitting relays effective when energized to disconnect the track relay means from the section rails and to connect a source of energy to the section rails. Front contact repeater relays are provided for each of the track relays, and the snubbing circuits for the front contact repeater relays are governed by back contacts of the front contact repeater relays for the other track relays. -A back contact repeater relay is governed jointly by each of the track relays and its associated front contact repeater relay 'to "detect code following operation of the track relays. -The transmitting relays are governed by the back contacts of the track relays and the control circuits for the transmitting relays include contacts of the front and back contact repeater relays for determining whether the transmitting relays will be steadily energized to transmit steady energy, or controlled by a back contact of the track relay for the adjacent section to transmit coded energy.

The accompanying drawing illustrates in 'a diagrammatic manner a stretch of railway track equipped with coded track circuit apparatus embodying my invention.

' Refer-ringto the drawing, .there'is shown a stretch of single track railway extending between two pas-sing siding's, and having wayside signals S2 and S4 for governing movements of traffic into the single track stretch between thesidings as illustrated diagrammaticallyon. the drawmg.

For the purpose of governing the operation of the wayside signals or for such additional functions as may be required, such as, for example, as indicating to an operator at each end of the stretch when the stretchis unoccupied, the two track sectionscomprising the stretch are each equipped with coded track circuit apparatus which functions to transmit steady or coded energy in either direction through the stretch. Since the apparatus embodying my invention may be used in conjunction with a number of different types of railway signaling systems of the coded track circuit type, only the necessary essentials have been shown in detail, and it will be understood by those skilled in the art that the circuit arrangements shown at each end of the stretch may be modified to provide any necessary type of operation.

Considering the apparatus in detail, the equipment located at the left-hand end of the stretch includes two polar biased code following track relays designated by the referencecharacters LNTR and LRTR, These relays impulses of negative relative polarity will cause operation of. the contacts of relay LRTR. A transmitting relay -2CR is shown controlled over a manually operated switch 5, arranged in such manner that the switch can occupy any I one, of three different positions, depending upon whether or not the transmitting relay ZCR is to be continuously energized, energized by impulses of energy supplied from 4 a continuously operating coding device CT, or deener- 'gized. When the contact. a ofthe transmitting relay ZCR is released it establishes the connection of the track relays L T s n LR -t h ls o seat n L11 nd wh n hi picked up it connects a track battery LATB acrossthe rails of section at the left-hand end thereof. Energy for the operationof the apparatus other than the track circuit-s is furnished by a suitablesouree of lowvoltage energy, such as a battery LB, having-positiveand negative terminals designated by the reference characters B and N respectively. Such a source wouldnorr ally beprovided at 3 each apparatus location.

The contacts of the polarized code following track re- :iays and LRTR may be utilized in connectionwith control circuits for governing the operation of the.;way-

. side signal SZ in such manner that the signal 52 is governedto its clear or proceed aspect when the contacts of one or the other of the polarized code following track relays are recurrently operated. These contacts may also 2 govern additional'circuits for indicating, for example, that the stretch of track extending between signals S2 and S4 is not occupied by a train or vehicle. From the foregoing, it will be apparent that the apparatus shown at the left-hand end of the stretch is capable of receiving impulses of coded energy supplied from the opposite end of the track section LT, which impulses may be either of apositive or negative relative polarity, and also, the

apparatus is capable of supplying to the section LT energy which is steady or coded, depending upon the condition of the-control switch 5. Although the control switch 5 is here-shown as a manually operated sw-itch,.for purposes of simplifying the disclosure, it is apparent'that switch 5 may be replacedby the contacts of relays which are governed by traflicconditions, or by remote control by a central operator. These features form no part of my invention,

and are therefore not. illustrated herein.

Considering now the apparatus shown at the right-hand end of thesingle track stretch, the apparatus at this location is somewhat similar to that shown at the left-hand end .of thestretchr The apparatus includes a code-following track relay RTR, a transmitting relay 4CR governed by circuits including the manually operable switch 7 so that the transmitting relay is either continuously'ener'gized,

energizedby coded energy supplied over a circuit illCllld'. :iuga contact .of the coding device CT, or .deenergized.

The transmitting relay functions to connect the winding of the code following track relay RTR-across the rails of section RT at the right-handend thereof when relay 4,08 is deenergized, and when relay 4CR is energized, I

enellgy is supplied to the track section RT from track battery RAT B,-.thepolarity of this energy being dependent upon. whether or notrelay 4PC which is governed by a manually operable switch 9, is picked up or released. It

will be seen therefore that the apparatus at the righthand end of the stretch is arranged'to receive coded usual low voltage source LB.

picked up at this time. picked up, an obvious circuit is established for supplying nfi he rs the etch, the. arta getncntof which comprises the essence of my invention, it will be apparent from the foregoing description that the apparatus at this location must be arranged in such manner as to retransmit steady energy received from either of the track sections LT or RT to the adjacent track section, or to retransmit coded energy received from one of the track sections to the adjacent track section. The apparatus is arrangedso that the on period of the transmitted code impulses occurs during the cit period of the received code impulses. As previously pointed out, the apparatus must not falsely transmit energy which isditferent fromthe energy received, which might occur as a result of energy feeding over broken down insulated joints 'at the cut section location. 3

The apparatus at the cut section includes a polar-biased code following track relay LTR associated with section LT, two polar biased code following track relays RNTR and RRTR associated with track section -RT, re1ay RNTR being designated as the normal track relay, andrelay RRTR being designated as the reverse track relay, two transmitting relays LOR and RCR associated with sections LT and RT respectively, and front cont-act repeater relays RTNF P, RTRFPand LTF P, associated with relays RNTR, RRTR and LTR, respectively. A back contact repeater relay TBP is governed by the code following operation of any one ofthe three code following track relays, as will .be made clear from the following detaileddescription.

The energysupplied to the sections LT and RT from the cut section apparatus is furnished by the batteries LTB and RTB, and energy for the operation of the circuits other than the'coded track circuits is furnished byxt-hc It will be noted that the relays whichare of thecode following type, whether in continuous coding operation or not, have their contacts indicated by a full line for one position and a dashed line for the other position. It is also to benoted that the contacts of relays which are at times slow, in releasing their contacts are indicated by a downwardly directed arrow as shown in the drawing.

For the purposes of retarding the release of these relays attirnes, a plurality of snubbing rectifiers, such as rectifiers .K1, K2, K3 and K4 are provided, which rectifiers, when connected across the winding of the associated relay,

function'in a well-known manner to increase the release .time of the relays.

It is believedthat a full understanding of my invention may be had by considering the detailed operation of the apparatus under the various conditions encountered-in -its operation. i

Let it first be assumed that with no train occupying the section between the signals S2 and S4, steady or non-coded energy is to be supplied at the left-hand end of the stretch and transmitted therethrough to the right-hand end of the stretch, Accordingly, the switch Sis operated to its uppermost-- position, in which it establishes an obvious circuit for continuously energizing the transmitting relay ZCR. With contact a of relay ZCR continuously picked up at this time, the positive terminal of track battery LATB is connected to track rail -1 of section LT, while the negative terminal is connected to track rail 2 of section'LT, At the cut section location, energy supplied over the rails of sect-ion LT flows from rail 1 over back contact a of transmitting relay LCR, through the winding of relay LTR-from left to right, and over rail. 2 ofscction LT backto the left-hand end .of the section. vAccordingly, the contacts of relay LTR will be continuously With contactb of relay LTR energy to relay LTFP. With contact 15 of relay LTFP picked up acircuit is established for energizing transwinding of relay RCR from left to right, over back con- 'tactd of-relayi RTNFP, and over-back contact a of-rclay TBP to terminal N. With contact a of relay RCR continuously picked up, the rails of section RT are connected to the battery RTB so that steady energy supplied at the left-hand end of section RT flows over the section rails to the right-hand end of the section. At this end of the section, the energy flows from track rail 2 over back contact a of relay 4CR, through the winding of relay RTR from right to left, and thence over rail 1 of section RT to the negative terminal of battery RTB at the left-hand end of the section, and relay RTR is accordingly continuously energized. At this time, relay 4CR will be continuously released with switch 7 occupying its lower-most position, as shown on the drawing.

From the foregoing, it will be apparent that the appar-atus at the cut section causes the retransmission of steady energy from left to right, when steady energy is received over section LT from the left-hand end of the stretch. As pointed out earlier, the reception of steady energy at the right-hand end of the stretch is indicated by the continuously picked up condition of the contacts of RTR, which condition may be utilized to indicate, for example, the direction of intended trafiic movement, clear block" indication, or other indication of traffic condi tions.

Let it now be assumed that it is desired to transmit steady energy from the right-hand end of the stretch to the left-hand end of the stretch. Accordingly, the switch will be operated to its lowermost position, in which position the supply of energy to winding of relay 20R is cut off, so that contact a of relay 2CR releases and remains released. The circuit for supplying energy from battery LATB to the track section LT is accordingly interrupted, and at this time the back contact a of relay 2CR connects the windings of relays LNTR and LRTR in series across the track rails 1 and 2 of section LT. At the cut section location, the interruption of the supply of steady energy to the winding of track relay LTR results in the contacts of this relay releasing and remaining released.

When contact b of relay LTR releases, a circuit is established for momentarily picking up the contacts of relay TBP, which circuit includes the back contact b of relay LTR, front contact a of relay LTFP, back contact b of relay RTNFP, and back contact 0 of relay RTRFP. Relay LTFP is slow in releasing its contacts at this time, since its snubbing rectifier K3 is connected across the relay winding by a circuit including back contact c of relay RTNFP and back contact d of relay RTRFP. Relay TBP is slow in releasing at this time, since the snubbing rectifier K4 is connected across the relay winding by the circuit including back contact b of relay RTNFP and back contact c of relay RTRFP.

When the contacts of relay TBP pick up, the circuit previously traced for energizing relay RCR is interrupted at back contact a of relay TBP, but when this relay closes its front contacts, the circuit for energizing relay RCR is completed over back contact a of relay LTR, back contact a of relay RNTR, back contack b of relay RTRFP, and back contact a of relay RRTR to terminal N. Relay RCR is maintained picked up at this time, the transfer time of contact a of relay TBP being sufficiently short to cause relay RCR to maintain its contacts picked up during the transfer of the contact a of relay TBP. However, after a short time interval, relay LTFP will release, and its front contact a will interrupt the circuit for energizing relay TBP, so that this relay will release aftter a short time interval. Additionally, when contact b of relay LTFP releases, the circuit previously traced for energizing transmitting relay RCR is interrupted and relay RCR releases, thereby disconnecting the track battery RTB from the rails at the left-hand end of section RT andconnecting the windings of track relays RRTR and RNTR in series across the section rails. I

At the right-hand end of the section, the interruption of the supply of energy to the winding of relay RTR from the section RT causes this relay to release, and any circuits controlled thereby will so indicate this condition; The switch 7 is'now moved to its uppermost position, and relay 4CR will be continuously energized by an obvious circuit: With contact a of relay 4CR picked up, energy is supplied to the rails of section RT and the windings" of the relays RRTR and RNTR at the lefthand end'of the section by a circuit which may be traced from "positive terminal of battery RATB, over back contact a of relay 4PC, which is considered to be deenergized at this time because switch 9 is open, over front contact a of relay 4CR, over rail 2 of section RT, over back contact a of relay RCR, through the windings of relays RNTR'and RRTR from right to left, over rail 1 of section RT, and over back contact b of relay 4PC to the negative terminal of battery RATB. The direction of flow of energy through the windings of relays RRTR and RNTR at this time is such that the contacts ofrelay RNTR will become picked up and the contacts of relay RRTR will remain released.

At this time, relay RTNFP is energized by. a circuit which may be traced from terminal B, through the winding of relay RTNFP, over front contact a of relay RNTR, back contact b of relay RTRFP, and back contact a of relay RRTR to terminal N. Accordingly, the contacts of relay RTNFP will be continuously picked up at this time.

Additionally, a circuit is established for energizing relay LQR, which circuit may be tracedfrom terminal B at back contact/b of relay LTR, over back contact c of relay LTFP, through the winding of relay LCR from left to right, over front contact at of relay RTNFP, and Over back contact a of relay TBP to terminal N. At the left-hand end of the stretch, relays LNTR and LRTR are energized at this time by a circuit which may be traced from the positive terminal of battery LTB, over front contact a of relay RTNFP, front contact a of relay LCR, rail 1 of section LT, back contact a of relay ZCR, through the windings of relays LNTR and LRTR from left to right, rail 2 of section LT, and back contact a of relay RTRFP to the negative terminal of battery LTB. The direction of current flow through the windings of relays LNTR and LRTR at this time is such that contacts of relay LNTR will be continuously picked up, while the contacts of relay LRTR will remain continuously released. 'As hereinbefore pointed out, this condition may be indicated by any one of several difierent arrangements to indicate a clear block condition to provide signal control, or to provide other indications of trafiic conditions within the stretch. It will be seen from the foregoing that the apparatus is arranged so that energy of a positive relative polarity supplied to the rails at the right-hand end of the stretch is repeated by the apparatus at the cut section to energize the track section at the left-hand end of the stretch, and thereby energize the track relay at the lefthand end of the stretch with energy of positive relative polarity.

If the supply of energy at the right-hand end of the stretch is interrupted by operation of the switch7 to its lowermost position, contact a of relay 4CR will release, so that the supply of energy to the rails of section'RT from battery RATB will be cut 01f. The consequent release of relay RNTR at the left-hand end of section RT establishes a circuit for momentarily energizing relay TBP, which circuit may be traced from terminal B at back contact b of relay RNTR, over back contact b of relay RRTR, front contact b of relay RTNFP, back contact a of relay LTFP, and through the winding of relay TBP to terminal N. Since back contacts a and ,b of relay LTFP are closed at this time, the snubbing rectifiers K4 and K1 are connected across the windings of relays TBP and RTNFP, respectively, so that these relays are rendered slow in releasing their contacts. When contact a of relay TBP picks up, the connection of the winding of relay LCR to terminal N of the source is changed 7 fromfback-icontact,;a of relay TBP to. a circuit which includes back contact a of relay LTR," backi'contact'n of relay RNTR, back contact b of relay LRTRFP and back contact "a of relay RRTR to terminal N. Relay LCR willremain picked up at this time, since the momentary interruption of the supply of energy to the winding during the transfer time of contacta of relay TBP is sufiicientlyshort that relay LCR willcon'tinue' to have its-contacts picked up during the, short interval.

' However, the release of contact aof relay'RNTR 'interrnpts the circuit previously traced for supplying energy to thewinding'of relay RTNFP, and after the expiration of a predetermined time interval .caused by the connection of the fsnubbing rectifier'Kl across .the winding of relay RTNFP, the contacts of relayRTNFP will release. When thejcontact d of relay-RTNFP releases the circuit for en'ergigin'gfthe Winding of relay LCR is interrupted, and accordingly the contacta of relay LCR will release, thereby interrupting the supply of energy to the rails of section LT, so that relay LNTR at the left-hand end of the section willfrelease. and remain released. From the foregoing, it will be apparent that the cut section apparatus shown comprising my invention is capable of retransmitting steady energy of positive relative polarity from section RT] to section LT.

Let it now be assumed that coded energy is to be transmitted through the stretch from the left-hand end to the rightwh'and end. Accordingly, switch. 7 will be operated toits lowermost position, and switch 5 at the left-hand end offthep'stretch is operated to its center or intermediate position, in which a circuit is established for supplying energy to the Winding of relay 20R, this circuit including a contact a of the continuously operating coding device CT which is recurrently operating its contacts at a predeterminedrate, say, for example,-75 times per minute. It will be apparent therefore that the contact a of transmitting relay ZCR is operated at a corresponding rate, so, that this-contact recurrently connects the battery LATB across therails of section LT at the left-hand end thereof. The supply of recurrent impulses of energy from battery LATB is supplied over the rails of section LT to the winding of relay LTR, so that the contacts of relay LTR are recurrently operated at this time.

Each time that the contact b of relay LTR is picked up, the circuit for energizingrelay LTFP is established, and, since contact c of relay RTNFP and contact d of, relay RT-RFP are released, the rectifier and snub K3 is connected across the winding of relay LTFP so that this is rendered sufficiently slow in releasing to bridge the intervals in which no energy is supplied to the windings. Accordingly, at; this time relay LTEP will be continuously picked up. Each time, that contact b of relay LTR releases, a circuit is established for supplying energy to thewinding of relay TBP, which circuit may be traced from terminal B at back "contact b of relay LTR, over front contact a of relay LTFP, back contact [1 of relay RTNFP, back contact of relay RTRFP, and through the winding of relay TBP to terminal N. Rectifier snub K4 will be connected across the'winding of relay TBP by the circuit including back contact b of relay RTNFP and back contact 0 of relay RTRFP, so that relay TBP is rendered sufficiently slow in releasing to. bridge the intervals in which no energy is supplied to the winding due to contact b of relay LTR being in its picked up position.

Withrelays LTFP and TBP picked up, a circuit is established for supplying energy to the winding of the transmitting relay RCR, which circuit may be traced from terminal B at front contact b of relay LTFP, through the winding of relay RCR, over back contact (I of relay RTNFP, front contact a of relay TBP, back contact a of F relay LTR, back contact a of relay RNTR, back contact b of relay RTRFP, and over back contact a of relay RRTR to terminal N. Since this circuit is closed only when relay LTR is released, it will be seen that the confact a of relay RCR is picked up each time that the con- I tacta of relay LTR is released; Whenconta'ct a of relay RCR' picks up, energy is suppliedfrom the battery RTB to the rails of section RT. it will be seen that these. im pulses of energy are supplied during the off periods'of the coded energy which is received from track section LT, so that the equipment at this time is functioning as a back contact coding cut section in which the impulses of energy received from one track circuit are retransmitted to the adjacent track circuit during the "o periods of the received impulses. The impulses of energy supplied to the section RT at the left-hand end thereof cause the recurrent operation of the contacts of relay RTR at the righthand end of the section, which recurrent operation may be detected by any of the well known arrangements used in the art, for the control of the signal S4, or for other traffic governing functions as desired.

Let it now be assumed that coded energy having a positive relative polarity is to be transmitted from the right-hand end of the stretch to the left-hand end of the stretch. Accordingly, switch 5 at the left-hand end of the stretch will'be operated to its lowermost position, in which the winding of relay ZCR is deenergized so that its contact a remains continuously released to connect the windings of relays LNTR and LNRTR in series across the rails of section LT at the left-hand end thereof. At the right-hand end of the stretch, the switch 9 will be open, so that relay 41 C will be released, and switch.7 will be operated to its center or intermediate position, so. that relay 4CR is recurrently energized by energy supplied over a circuit including contact a of the continuously operating coding device CT. Accordingly, at this time impulses of energy will be supplied over the rails of section RT to energize the windings of relays RNTR and RRTR by a circuit which may be traced from positive terminal of battery RATB, over back contact a of relay 4P0, front contact a of relay 4CR, rail 2 of section 1T, back contact a of relay RCR, through the windings of relays RNTR and RRTR from right to left, rail 1 of section RT, and over back contact 12 of relay 4PC to the negative terminal of battery RATB. As a result the contacts of relay RNTR will be recurrently picked up and released in response to the supply of coded impulses of energy supplied to the relay winding, while the contacts of relay RRTR will remain continuously released at this time since the flow of current therethrough is in the direction which Wiil not pick up the contacts of the relay.

With the contacts of relay RNTR recurrently operating, a circuit is established for supplying energy to the winding of relayRTNFP, this circuit being traced from terminal B through the winding of relay RTNFP, over front contact a of relay RNTR, back contact b of relay RTRFP, and back contact a of relay RRTR to terminal N. The snubbing rectifier K1 is connected across the winding of relay RTNFP at this time by a circuit including back contact b of relay LTFP, so that relay RTNFP is rendered sufficiently slow in releasing to bridge the short intervals in which contact a of a relay RNTR is open. Relay TBP is supplied with energy each time that contact I) of relay RNTR is released, by a circuit which may be traced from terminal B at back contact I; of relay RNTR, over back contact [2 of relay RRTR, front contact b of relay RTNFP, back contact a of relay LTFP, and through the Winding of relay TBP to terminal N. Snubbing rectifier K4 is connected across the winding of relay TBP through the back contact a of relay LTFP, so that relay TBP will remain picked up during the short intervals in which contact b of relay RNTR is picked up. Accordingly, it will be seen that at this time the relays RTNFP and TBP are both picked up as a result of the recurrent operation of the contacts of normal track relay RNTR.

Relay LCR is supplied with energy at this time by a circuit which may be traced from terminal B at back contact bof relay LTR, over back contact c of relay LTFP, through the winding of relay LCR, over front contact 0. of relay RTNFP, front contact a ofrelay TBP,

back contact a of relay LTR, back contact a of relay RNTR, back contact b of relay RTRFP, and back contact a of relay RRTR to terminal It will be seen that this circuit is closed each time contact a of relay RNTR occupies its released position, so that relay LCR is picked up during the intervals that relay RNTR is released, and vice versa.

Energy is supplied to track section LT at this time by a circuit which may be traced from the positive terminal of battery LTB, over front contact a of relay RTNFP, front contact a of relay LCR, rail 1 of section LT, back contact a of relay ZCR, through the windings of relays LNTR and LRTR from left to right, rail 2 of section LT, and back contact a of relay RTRFP to the negative terminal of battery LT B. It will thus be seen that section LT is supplied with impulses of coded energy having a positive relative polarity at this time, which energy causes the operation of the contacts of relay LNTR, such operation being detected by the usual code detecting apparatus to provide control for the wayside signal S2 or such other functions that may be desired. Thus the positive polarity coded energy supplied to the right-hand end of the stretch is repeated to the left-hand end of the stretch by the apparatus at the cut section location, the arrangement being such that the on impulses of coded energy for section LT occur during the off periods of the energy supplied to section RT.

If the switch 9 at the right-hand end of the stretch is closed at this time, the contacts of relay 4PC will pick up and thereby reverse the polarity of the impulses of energy supplied to the section RT from battery RATB. Accordingly, at the cut section location, relay RNTR will have its contacts continuously released while the contacts of relay RRTR will be recurrently picked up and released in response to the coded impulses of energy supplied thereto. Under this condition, the relay RTRFP will be energized by a circuit which may be traced from terminal B at back contact b of relay RNTR, through the winding of relay RTRFP, and over front contact a of relay RRTR to terminal N. Snubbing rectifier K2 is connected across the winding of relay RTRFP at this time through the back contact d of relay LTFP, so that relay RTRFP is rendered sufficiently slow in releasing its contacts to bridge the momentary intervals in which contact a of relay RRTR is released. Relay TBP is energized at this time by a circuit including back contact b of relay RNTR, back contact b of relay RRTR, front contact c of relay RTRFP, back contact b of relay RTNFP, back contact a of relay LTFP and the winding of relay TBP. Snubbing rectifier K4 is connected across the winding of relay T BP through back contact a of relay LTFP, so that relay TBP will be picked up at this time and will remain picked up in the short intervals in which the contact b of relay RRTR is picked up.

With relays RTRFP and TBP picked up, a circuit is established for recurrently energizing the winding of the transmitting relay LCR. This circuit may be traced from terminal B at back contact b of relay LTR, over back contact c of relay LTFP, through the winding of relay LCR, over front contact b of relay TBP, front contact 'b of relay RTRFP, and back contact a of relay RRTR to terminal N. It will be seen that relay LCR is accordingly picked up each time that relay RRTR releases its contacts, and relay LCR releases its contacts each time that relay RRTR picks up. As a result, impulses of energy are supplied to the track circuit LT at this time and to the winding of relay LRTR at the left-hand end of the stretch by a circuit which may be traced from the positive terminal of track battery LTB, over front contact a' of relay RTRFP, rail 2 of section LT, through the windings of relays LRTR and LNTR from right to left, over back contact a of relay 2CR, over rail 1 of section LT, front contact a of relay LCR, and back contact a of relay RTNFP to the negative terminal of battery LTB. The impulses of energy supplied over the rails of section LT- 10 cause the recurrent operation of the contacts of the reverse code following track relay LRTR 'at the left-hand end of the section, which code following operation may be detected by suitable means to govern the operation of the signal S2 or to control other functions.

From the foregoing description, it will be apparent that the apparatus at the cut section location arranged in accordance with my invention is capable of transmitting steady energy in either direction through the stretch, and is also capable of transmitting coded enengy in one direction with a given polarity, and in the other direction with either one of two relative polarities. The appa ratus is arranged so that when coded energy is being retransmitted by the apparatus at the cut section, the code impulses fed to the receiving track circuit at that loca} tion occur during the off periods of the codeim-v pulses received from the adjacent track circuit atthat time.

As previously pointed out,-one of the principal .fea tnres of my invention is the provision of snubbing cit;

' cuits for the front contact repeater relays of the code following track relays at the cut section, which snubbing circuits are governed by back contacts of the front con tact repeater relays for the adjacent section. That is, the snubbing circuits including rectifiers K1 and K2 for snubbing relays RTNFP and RTRFP are governed by back contacts of relay LTFP, whereas the snubbing' cir cuit for relay LTFP including rectifier K3 is governed by back contacts of relays RTNFP and RTRFP. This cross check of the snubbing circuits provides several distinct advantages in operation of the apparatus and in protection against faulty operation due to insulated joints which may break down to cause the leakage of energy from one of the track circuits to the adjacent track relays.

The arrangement of the snubbing circuits for the front contact repeater relays in the manner described is particularly advantageous during the time that the system is being cleared out by transmitting steady energy from one end of the section while coded energy is being sup; plied from the other end of the section. This action may be best described by assuming that coded energy is being supplied from the right-hand end of the stretchtothe rails of section RT, so that relay RNTR, for example, is being operated by the coded impulses of energy. Ac cordingly, as previously described, this enengy will be retransmitted by the apparatus of the cut section into the rails of section LT, the on periods of the retransmitted code occurring during the 01f periods of the received codes. Now let it be assumed that steady energy is supplied to the left-hand end of the stretch, so that relay LTR picks up its contacts during the first interval in-which an on impulse of energy has picked up the contacts of relay RNTR, and contact a of code transmitting relay LCR is released. In such an instance, contact b of relay LTR will close the circuit for energizing the winding of relay LTFP, with the result that this relay will pick up. When relay LTFP picks up, its contact a interrupts the snubbing circuit including rectifier K4, so that relay TBP will release quickly, the circuit for energizing the winding of relay TBP being interrupted also by contact a of relay LTFP. When relay RNTR releases at the end of the code pulse, the circuit for supplying energy to the winding of relay RTNFP is inter rupted at front contact a of relay RNTR, and since the snubbing circuit for relay RTNFP is interrupted by contact b of relay LTFP, relay RTNFP will releasequickly. A circuit is now established for energizing relay RCR, which circuit may be traced from terminal B at front contact b of relay LTFP, through the winding of relay RCR, over back contact d of relay RTNFP, and back contact a of relay TBP to terminal N. Accordingly, the contact a of relay RCR will pick up and remain picked up to continuously connect the battery RTB across the section rails, to thereby supply steady energy to the rails arsenic o'f'sec'tion RT 'at the left-hand end thereof. When this energy picks up the contacts of relay RTR at theirighthand end of the stretch, circuits, not shown, may be employed to interrupt the supply of energy to the winding of relay 4CR, so that relay 4CR will remain released at this time. It will be seen from the foregoing that the use of the back contacts of the front contact repeater relays in the control of the opposite front contact repeater relays provides an arrangement whereby steady energy supplied toone end of the stretch is quickly repeated through the cut section to the other end of the stretch, without the delay occasioned by the slow release periods of the front contact repeater relays, since by opening the Snubbing circuits,v :these relays are caused to release quickly to thereby establish the circuits for repeating the steady energy into the receiving track section. The action of the'apparatus when steady energy is being transmitted from right to left, with coded energy in the lefthand section of thestretch, is similar to that described above and need not be pointed out in detail.

The front contact repeaters RTNFP and RTRFP are provided with control circuits which not only check that the corresponding front contact of the code following track relay is closed, but also check that the back contact of the track relay responsive to the opposite polarity is closed, so that the operation of the contacts of the track relay for opposite polarity will cause the front contact repeater relay for the other code following track relay who released. This provision makes it possible to guard against faulty operation due to energy feeding over insulated joints which are broken down sufficiently to allow enough current to pass therethrough to operate the track relay for the adjacent section. To illustrate this protection, let it be assumed that coded energy of a negative relative polarity is being received from section RT. Accordingly, as previously pointed out, the code following track relay RRTR will be recurrently operating its contacts with the result that the associated front contact repcater relay RTRFP and the back contact repeater relay TBP will be energized, and relay LCR will be recurrently energized by a circuit previously traced, including a back contact of relay RRTR, so that each time that relay RRTR releases, contact a of relay LCR picks up to connect the battery LTB to thetrack section. The track circuit connections are staggered, so that with the incoming code pulses in section RT having a polarity such that the uppermost rail or rail 1 of section RT is positive with respect to rail 2, the code impulses supplied to the section LT from battery LTB will have a polarity such that the lower rail 2 is positive with respect to the upper rail 1. Under such a condition, if the insulated joints 3 atthe cut section should be defective, energy supplied frombattery LTB will feed over these joints to cause current to How through the windings of relays RRTR and RNTR, and it will be seen that the relay RNTR will become picked up by a circuit which may be traced from the positive terminal of battery LTB, over front contact a of relay RTRFP, rail 2. over insulated joint 3 therein, over back contact a of relay RCR, through the windings of relays RNTR and RRTR from right to left, over rail K through the insulated joint 3, over front contact a of relay-LCR, back contact a of relay RTNFP to the negative terminal of battery LTB. Thus the contacts of relay RNTR will be picked up when the contacts of relay RRTR are released and relay LCR is picked up. When contact 1.: of relay RNTR picks up it interrupts the circuit for supplying energy to the winding of relay RTTRFP, and additionally interrupts the snubbing circuit which is completed through back contact at of relay LTFP at thistime, so that relay RTRFP will immediately release. and the circuit for ,energizingrelay LCR will .be opened at front contact b of relay RTRFP, resulting in the consequent. release of contact a of relay LCR, therebyterminating the code impulse. The reception of the next code impulse from section RT which is elfective to all) operate relay RRTR will cause relay 'RTRFP to again pick up, with consequent repetition of the cycle described above. Accordingly, it will be seen that under such conditions the supply of energy to section RT from battery LTB will consist 'of pulses of energy which have a very small on time compared with the code pulses supplied thereto under normal conditions. It will also be apparent that such pulses will occur at no greater frequency than the frequency of the received code pulses. The supply of code with very short on time to section L'l will result in the track relay LRTR being operated for such short intervals that the code detecting apparatus associated therewith will not usually respond to such operation, so that the failure in this case is on the side of safety. In any event the code impulses of negative polarity, transmitted to the adjacent section will never occur at a frequency greater than the frequency of the received impulses. This condition is true for coded energy of any frequency, steady energy, or no energy. Thus it is not possible for received code of cycles per minute frequency having a negative polarity, to be retransmitted at, say, code having a frequency of cycles per minute, which might cause false operation of the code detection apparatus.

Since, with relay RTRFP energized, the control circuit for transmitting relay LCR is independent of the back contact a of relay RNTR, it will be seen that the operation of the contacts of relay RNTR caused by the energy feeding over the broken down joint cannot cause relay LCR to recurrently pick up and release its contact to thereby generate a so-called door-bell code.

It should also be noted that relay RTNFP cannot pick up unless relay RTRFP is released and relay RNT R is.

picked up. Under the conditions described above, relay RNTR is picked up for only a very short interval after the release of relay RTRFP, so that relay RTNFP :is not supplied with sufficient energy to enable it to pick up. Since energy of positive polarity can be supplied to section LT only when relay RTNFP is picked up, it will be apparent that the polarity of the energy supplied to section LT,with the joints broken down, cannot be changed from negative to positive.

From the foregoing description, it will be seen that with the apparatus for the back contact coding cut section arranged in accordance with my invention, steady energy may be repeated from one track circuit into the other, or coded energy may be supplied from one track circuit to the other, without the risk of an unsafe condition caused by the breakdown of the insulated joints between the track sections.

Although Ih'aveherein shown and described only one form 'of coded track circuit apparatus embodying my invention, it will be apparent that various changes and modifications may be made therein within the scope-of the appended claims without departing from the spirit and scope of my invention.

Having thus described my invention, what I claim is:

1. Ila-combination, a first and a second adjacent section of railway track, means at the remote end of each of said sections for at times supplying steady energy to the rails of 'said section,- for at other times supplying coded energy to the rails of said section, and for at still other times connecting track relay means across the rails of said section at the remote endthereof, and repeating means at the adjacent ends of said first and said second sections for retransrnitting energy supplied to oneof said sections at the remote endthereof to the remote end of the adjacent section, said repeating means comprising a first and a second-track relay associated with, said first and said second sections respectively, said track relayshavingfront and back contacts .which are closed according as energy is or is not supplied to a winding of'the ,trackrelay from the associated track section, a first and a second front contact repeater relay associated with .said first and said second track relays respectively, a control circuit for each of said front contact repeater relays including a front contact of the associated track relay, a back contact repeater relay, a control circuit for said back contact repeater relay including back contacts of said first and said second track relays and front contacts of said first and said second front contact repeater relays, a first and a second transmitting relay associated with each of said sections and effective when energized to supply energy to said first and said second sections respectively, a first control circuit for said first transmitting relay including a front contact of said second front contact repeater relay and a back contact of said back contact repeater relay, a second control circuit for said first transmitting relay including a front contact of said second front contact repeater relay, a front contact of said back contact repeater relay, and a back contact of said second track relay, a first control circuit for said second transmitting relay including a front contact of said first front contact repeater relay and a back contact of said back contact repeater relay, a second control circuit for said second transmitting relay including a front contact of said first front contact repeater relay, a front contact of said back contact repeater relay, and a back contact of said first track relay, a snubbing circuit for said first front contact repeater relay including a back contact of said second front contact repeater relay, and a snubbing circuit for said second front contact repeater relay including a back contact of said first front contact repeater relay.

2. In combination, a first and a second code following track relay having front and back contacts which are closed according as energy is or is not supplied to a winding of the relay, a first and a second front contact repeater relay associated with said first and said second track relays respectively, a control circuit for each of said front contact repeater relays including a front contact of the associated code following track relay, and a snubbing circuit for each of said front contact repeater relays including a back contact of the other front contact repeater relay.

3. In combination, a first and a second adjacent section of railway track, means at the remote end of said first section for at times supplying steady energy having a first relative polarity to the rails of said section, for at other times supplying coded energy having said first relative polarity to the rails of said section, and for at still other times connecting polarity-responsive track relay means across the rails of said section at the remote end thereof, means at the remote end of said second section for at times supplying steady energy having a first relative polarity to the rails of said section, for at other times supplying coded energy having a first or a second relative polarity to the rails of said section, and for at still other times connecting track relay means responsive to said first relative polarity across the section rails, and cut section apparatus located at the adjacent ends of said sections for repeating the energy supplied to one of said sections to the other of said sections comprising a first track relay responsive to energy ,of said first relative polarity, said first track relay having front and back contacts which are closed according as energy having said first relative polarity is or is not supplied to a winding of the relay, second track relay means including normal front and back contacts which are closed according as energy having said first relative polarity is or is not supplied to said track relay means and reverse front and back contacts which are closed according as energy having said second relative polarity is or is not supplied to said track relay means, a first transmitting relay having a contact which when released connects said first track relay across the rails of said first section and when picked up connects a source of energy across the rails of said first section, a second transmitting relay having a contact which when released connects said second track relay means across the rails of said second section and when picked up connect a source of energy across the rails of said second '14 section, a first, a second and athirdfront contact repeater relay, said first front contact repeater relay being controlled by a circuit including a front contact of said first track relay, said second front contact repeater relay being controlled by a circuit including a normal front contact of said second track relay means, a back contact of said third front contact repeater relayand a reverse back contact of said second track relay means, said third front contact repeater relay beingcontrolled by a circuit including a normal back contact of said second track relay means and a reverse front contact of said second track relay means, a snubbing circuit for said first front contact repeater relay including back contacts of said second and third front contact repeater relays, a snubbing circuit for said second front contact repeater relay including a back contact of said first front contact repeater relay, a snubbing circuit for'said third front contact repeater relay including a back contact ofsaid first front contact repeater relay, a back contact repeater relay governed by a first circuit including a back contact of said first track relay and a front contact of said first front contact repeater relay, a second circuit including a normal back contact of said second track relay means and a front contact of said second front contact repeater relay, and a tbird circuit including a reverse back contact of said second track relay means and a front contact of said third front contact repeater relay, a first control circuit for said first transmitting relay including a back contact of said first track relay, a back contact of said first front contact repeater relay, a front contact of said second front contact repeater relay, and a back contact of said back contact repeater relay, a second control circuit for said first transmitting relay including a back contact of said first track relay, a back contact of said first front contact repeater relay, a front contact of said second front contact repeater relay, a front contact of said back contact repeater relay, a normal back contact of said second track relay means and a reverse back contact of said second track relay means, and a third control circuit for said first transmitting relay including a back contact of said first track relay, a back contact of said first front contact repeater relay, a front contact of said back contact repeater relay, a front contact of said third front contact repeater relay and a reverse back contact of said second track relay means, a first control circuit for said second transmitting relay including a front contact of said first front contact repeater relay, a back contact of said second front contact repeater relay, and a back contact of said back contact repeater relay, a second control circuit for said second transmitting relay including a front contact of said first front contact repeater relay, a back contact of said second front contact repeater relay, a front contact of said back contact repeater relay, a back contact of said first track relay, a normal back contact of said second track relay means, a back contact of said third front contact repeater relay, and a reverse back contact of said second track relay means, and pole changing means including at least one contact of at least one of said second and said third front contact repeater relays for governing the polarity of the energy supplied to said first track section.

4. In combination, a first and a second adjacent section of railway track, means at the remote end of said second section for at times supplying coded energy to the rails of said section, said coded energy having a first relative polarity at times and a second relative polarity at other times, first track relay means located at the remote end of said first section and selectively responsive to coded energy of said first and said second relative polarity, and repeating means located at the adjacent ends of said first and said second sections for retransmitting energy supplied from the remote end of said second section to the remote end of said first section, said repeating means comprising second track relay means including normal front and back contacts which are closed according as energy having' 'said first relative polarity is or is not supplied to said track relay means and includingreverse front and back contacts which are closed accordingas energy having said second relative polarity is or is not supplied to said track relay means, a first and a second-front'contact repeater relay, a first circuit for energizing said first front contact repeater relay including a reverse 'front'contact and a normal back contact of said second track relay means, a second circuit for energizing said second front contact repeater relay including a normal front contact and a reverse back contact of said second track relay means and a back contact of said first front contact repeater relay, a transmitting relay, a third circuit for ener-- gizing said transmitting relay including a front contact of said first front contact repeater relay and a reverse back contact of said second track relay means, a fourth circuit'for energizing said transmitter relay including a front contact of said second front contact repeater relay and a normal back contact and a reverse-back contact of said second track relay means, a track battery, circuit connections including a front contact of said transmitting relay for connecting said track battery to the rails of said first section, and means including at least one contact of at least one of said front contact repeater relays for reversing the polarity of said circuit connections,

5. In combination, a first and a second adjacent section of railway track, means at the remote end of said second section for at times supplying coded energy to the rails of said section, said coded energy having a first relative polarity at times and a second relative polarity at other times, first track relay means located at the remote end of said first section and selectively responsive to coded energy of said first and said second relative polarity, and repeating means located at the adjacent ends of said first and said second sections for retransmittingenergysupplied from the remote end of said second section to the remote end of said first section, said repeating means comprising second track relay means including normal front and 16 back-contacts which are closed according as energy having said first relative polarity is or is not supplied to said track relay-means and including reverse front and back contacts contact-of said second track relay means, a second circuitfor energizing said second front contact repeater relay including a normal front contact and a reverse back contact of said second track relay means and a back contact of said first front cont-act repeater relay, a transmitting relay, a third circuit for energizing said transmitting relay including a front contact of said first front contact repeater relay and a reverse back contact of said second track relay means, a fourth circuit for energizing said transinitter relay including a front contact'of said second front contact repeater relay and a normal back contact and a reverse back contact of said second track relay means, a track battery, a circuit for supplying coded energy having said first relative polarity to the rails of said first section from said battery including a front contact of said second References Cited in the filetof this patent UNITED STATES PATENTS Thompson Feb. 28, 1950 Henderson June 26, 1951 

